Rechargeable metal-ion batteries, for example lithium ion batteries, are extensively used in portable electronic devices such as mobile telephones and laptops, and are finding increasing application in electric or hybrid electric vehicles.
Rechargeable metal ion batteries have an anode layer; a cathode layer capable of releasing and re-inserting metal ions; and an electrolyte between the anode and cathode layers. When the battery cell is fully charged, metal ions have been transported from the metal-ion-containing cathode layer via the electrolyte into the anode layer. In the case of a graphite-based anode layer of a lithium ion battery, the lithium reacts with the graphite to create the compound LixC6 (0<=x<=1). The graphite, being the electrochemically active material in the composite anode layer, has a maximum capacity of 372 mAh/g.
The use of a silicon-based active anode material, which may have a higher capacity than graphite, is also known.
WO2009/010758 discloses the etching of silicon powder in order to make silicon material for use in lithium ion batteries.
Xiao et al, J. Electrochem. Soc., Volume 157, Issue 10, pp. A1047-A1051 (2010), “Stabilization of Silicon Anode for Li-ion Batteries” discloses an anode comprising silicon particles and Ketjenblack carbon.
Lestriez et al, Electrochemical and Solid-State Letters, Vol. 12, Issue 4, pp. A76-A80 (2009) “Hierarchical and Resilient Conductive Network of Bridged Carbon Nanotubes and Nanofibers for High-Energy Si Negative Electrodes” discloses a composite electrode containing multiwall carbon nanotubes and vapour-grown nanofibres.
US 2011/163274 discloses an electrode composite of silicon, a carbon nanotube and a carbon nanofibre.
It is an object of the invention to provide an anode composition for a metal ion battery that is capable of maintaining a high capacity.
It is a further objection of the invention to provide a composition for forming an anode of a metal ion battery from a slurry.